DESCRIPTION: Atrazine is the most heavily used single herbicide in the USA with estimates of approximately 82 million pounds applied to crops each year. It has been detected with very high frequency in the water in the USA as well in many major aquifiers. Thus, farm families are likely exposed to some concentration of atrazine per os during a growing season and perhaps throughout the year. There is a relative paucity of published reports on the toxicity of atrazine despite its very high usage. Also, we were only able to find one published report on the immunotoxicity of atrazine. This report showed a persistent decrease in primary antibody response up to 40 days after the administration of a single dose of atrazine. Other immune parameters showed more transient effects. Thus, atrazine is immunotoxic in an adult exposed animal. Many substances have been shown to have greater or different immunotoxicity when administered during the gestation of the animal. The very high use levels of atrazine and the potential for women to ingest atrazine during the gestational development of their child create a case to determine whether atrazine can affect the normal development of the immune system. Therefore, this application seeks to test the hypothesis that prenatal exposure to atrazine will adversely affect the normal development of the immune system. This hypothesis will be tested by exposing gravid mice to atrazine throughout the gestational period. The offspring of these dams will be allowed to nurse their natural mother, weaned at d21 of life and a variety of immune parameters will be assessed beginning at 6 weeks of age. This duplicates the paradigm of a human ingesting atrazine during the gestation of her child, nursing the child and then assessing the immune response of the young adult offspring. This R21 application will be used to test the above stated hypothesis and provide data to justify mechanistics studies on the effect of prenatal atrazine exposure on the developmental immune response.